In the remedial marketplace, there is a problem with sites that are contaminated with certain materials.
Coal tar in particular has been generated over the years from various manufactured gas plants (MGP) around the country. The manufactured gas of these plants was produced by burning coal, which produced methane (coal gas). Coal tar, which was one of the byproducts generated by these plants, had little or no market value. Consequently, much of the coal tar was disposed on-site, either down wells or in gas holders in the plants, or shipped off-site and landfilled.
At ambient underground water temperatures, coal tar is a very thick and a viscous substance and therefore is not easily mobilized. Consequently, prior efforts to remove coal tar from soil has largely centered upon excavation. For example, one previous method adds acid to the soil, which solidifies the coal tar so it can be excavated as a solid. Another method mixes coal or wood with the coal tar prior to excavation.
Alternatively, the coal tar may be mobilized by thermal remediation. These methods are very costly and require the placement of in-situ electrodes or excavation followed by thermal desorption. In addition, the heating of the coal tar leads to the release of several volatile byproducts such as benzene, toluene, ethyl benzene, and xylenes (BTEX), and semi-volatile byproducts such as creosote and polyaromatic hydrocarbons, including benzo(a)pyrene (a known carcinogen).
Other known removal techniques, such as enzyme action and vacuum extraction, which have been successful in remediating other soil contaminants, are ineffective in the removal of heavy hydrocarbons and coal tar due to their high viscosity. Still other methods promote using surfactant flushing in combination with vacuum extraction. Although these methods can mobilize coal tar and heavy hydrocarbons, they require the injection of one or more surfactants as amendment compounds in combination with the oxidizers.
Methods of decontaminating soil and groundwater containing certain organic contaminants are disclosed in U.S. Pat. No. 6,843,618, entitled “IN SITU SUBSURFACE DECONTAMINATION METHOD,” invented by the inventor hereof, and incorporated by reference herein. However, the methods so disclosed are not able to efficiently remediate and emulsify coal tar and heavy hydrocarbons.
Thus, conventional technology has not provided a successful and cost-effective means by which to remediate coal tar and heavy hydrocarbons.
In addition to the above-referenced problems with sites that are contaminated with coal tar and heavy hydrocarbons, conventional remediation methodologies are also ineffective at removing contaminants in general from sediment. Numerous MGP sites are located in low-lying areas where sediments make up a significant mass of the geologic formation. These sediments present a major obstacle to nearly all in-situ chemical oxidation processes because of the extraordinarily high percentage of natural organic matter (NOM). This material is composed primarily of cellulose from decayed plants. This organic matter presents an unusually high matrix oxidizer demand (MOD) in comparison to soils composed primarily of inorganic minerals. Therefore, conventional oxidizers such as the Fenton's hydroxyl radical mechanism or persulfate systems, which are widely known for their highly reactive oxidation potentials, are inefficient in remediating contaminants located in sediment formations. The oxidation potential of these entities is such that they react with the sediments and contaminants equally well. Thus, they are indiscriminate in selecting contaminants from sediment.
Thus, conventional technology has not provided a successful and cost-effective means by which to remediate contaminants in general from sediment.